1. Field of the Invention
The present invention relates to a lens shape measuring apparatus for measuring an edge thickness of an eyeglass lens to be fitted into a lens opening of an eyeglass frame.
2. Description of the Related Art
A typical one of the conventional edge thickness measuring apparatuses used to edge an uncut lens is disclosed in Japanese Laid-Open Patent Publication No. Hei 7-314307 in which an edge thickness of an uncut lens for fitting into a lens opening of an eyeglass frame is measured using a freely rotatable feeler which is to be placed on a working locus on each of the front and rear surfaces of the lens, the working locus having a predetermined relationship to the lens opening (lens frame) or to a lens-shaped template.
This conventional apparatus was proposed to prevent the feeler from damaging the refracting surface of an uncut lens during measurement or prevent the feeler itself from being deformed or broken because of receiving a frictional resistance from the front or rear surface of the lens or lens-shaped template.
Especially, when measuring an edge thickness of an eyeglass lens having a stepped boundary (i.e., having a difference in surface level of the eyeglass lens) between a distance portion (farsighted portion) and a near portion (nearsighted portion) of the eyeglass lens (i.e., EX lens), a feeler will be caught by the stepped portion, and thus the edge thickness of the lens cannot be accurately measured if the feeler is merely slid in contact with the front or rear refracting surface of the lens during measurement. The conventional apparatus was provided to solve this problem.
However, in the conventional apparatus, there is still a fear that a feeler constructed of merely rotatable members cannot go beyond a stepped portion generated by a great difference in thickness between the distance and near portions of, for example, an EX lens, and will be caught by the stepped portion when the feeler is slid from the thin part to the thick part of the EX lens by the rotation of the EX lens.
Additionally, the conventional apparatus cannot determine the degree of a difference in surface level of an EX lens, and thus cannot accurately measure the edge thickness of the EX lens on the whole edge thereof.
As a result, it is impossible to produce an eyeglass lens having an exact fit to an eyeglass frame and provide nice-looking eyeglasses according to the taste of an eyeglass wearer.